Connecting to different DBMS's with isql

I want to connect to different DBMSs from one host. I've been told by Informix that the format is isql dbname@dbserver. The DBMSs I'm connecting to are set up by a third party software vendor and all we have is a run time license (we've got isql and dbschema only.) We don't currently have any sort of development environment. I looked on the various hosts for the DBSERVER environment variable. It is not set. I tried using the hostname instead, to no avail. I am using Informix SQL version 4.10.UC2. As far as the name of the Informix server installation -- I dunno.. I've just seen Informix.. No SE or Online or anything... Anyone able to give me some ideas? I want to connect to a database called test on a host named STORE123. Telneting to STORE123 and typing isql test works fine. Thanks! Herschel